1. Field of the Invention
This invention relates to electrical switching apparatus, and in particular, to such apparatus with multiple contact fingers and to a contact finger guide which maintains spacing between the contact fingers during current interruption and blocks passage of arcing gasses back along the contact fingers.
2. Background Information
Electrical switching apparatus for power distribution systems includes devices such as, for instance, circuit breakers, network protectors, transfer switches and disconnect switches. A common type of power air circuit breaker has a molded casing housing multiple pole assemblies all driven by a common operating mechanism. Each pole includes a contact arm carrier pivoted by the operating mechanism between open and closed positions. The contact arm carriers support contact arms having movable contacts which engage stationary contacts with the contact arm carrier in the closed position. Typically, the contact arm is made up of a number of contact arm laminations or contact fingers mounted on a common pivot pin on the carrier. Contact springs bias the contact fingers against the stationary contacts in the closed position to provide contact pressure and to accommodate for wear.
There is a need to locate the contact fingers laterally against magnetic loads during short circuit conditions. The contact fingers tend to sway from side to side due to the magnetic effects of adjacent poles which are out of phase. This allows the moving contacts to slide on the stationary contacts. During interruption, when the contact fingers are arcing, magnetic forces tend to pull the ends of the fingers together, toward the center of the pole. The fingers may bend, touch at their tips, and even weld together, losing their independent action. Separating fins may be molded into the carrier, but they are difficult to mold and often break during interruption. The taper required to mold them limits their effectiveness in locating the contact fingers. Also, there is a need to protect the contact springs from arc generated debris, which can collect between coils, limiting spring travel after interruption. The contact carrier partially shrouds the springs, but there must be enough clearance to allow the fingers to pivot to the fully compressed position.
There is a need therefore for an improved electrical switching apparatus with plural, parallel spaced contact fingers arranged to prevent bending and welding together of the contact fingers during arcing.
There is a further need for such an improved electrical switching apparatus which protects the contact springs and main contacts from arc gases and debris generated at separate arcing contacts.
There is an associated need for such electrical switching apparatus which achieves these results with simple, economical arrangements of the parts.